Electric field effects on relativistic charged particle motion in Tokamaks

Abstract

The authors consider the relativistic guiding center motion of charged particles (charge e, rest mass m₀) in magnetic fields consistent with toroidal Tokamak equilibrium. The particle acceleration due to the toroidal electric field-essential to Tokamak operation-is taken into account. For the case of weak acceleration (eU/m₀C²<<1, where U is the loop voltage), the poloidal locus of charged particle motion is found to be an envelope of closed drift orbits which, in the case of large aspect-ratio, are characterized by adiabatic invariance of their cross-sectional area. This allows, in the absence of collisions, a complete description of the motion and confinement of runaway electrons in Tokamaks. For peaked current distributions and sufficiently high energies drift separatices exist. They are calculated and their relevance to charge particle confinement and injection is considered.